The present invention relates to certain improvements in pipe or tube mills of the cage type such as shown in applicant's prior U.S. Pat. Nos. 3,323,341; 3,472,053; and 3,635,064. In such tube or pipe mills, the edge forming is usually applied to the strip as part of or immediately downstream of the main forming roll passes which are commonly called breakown passes. However, when the strip which is being formed into the tube or pipe begins to creep in a lateral direction or a direction perpendicular to the general flow of the strip, an uneven amount of edge forming may result. If the inboard and outboard edges are formed unequally, a poor seam weld will develop. In a high speed mill, this may not be detected until substantial substandard or scrap product is produced. Accordingly, any creep of the strip toward the inboard or outboard side of the mill may cause the two edges of the strip to be formed unevenly and sometimes one edge of the strip may creep out of the edge forming roll and not be edge formed at all. This, of course, results in either no weld seam at all or certainly a defective weld seam.
The causes of the strip creeping are many. For example, improper setting and improper roll contours are common causes of creeping, although they can be controlled. Sometimes uneven thickness of the strip at the two edges may initiate creeping. Most often the cause is the camber of the strip. By camber of the strip, it is meant that although the lateral edges of the strip may be of uniform width, they deviate symmetrically from the normal center line of the strip.
Also, in recent years, the demand for welded tubular goods tends toward tubes of lighter and lighter wall thickness on the one hand and heavier wall thickness on the other hand. At the same time, the material being rolled is stronger in yield strength. As a result, the function of edge forming becomes increasingly important and critical. Therefore, the purpose of the invention is to provide uniform and true edge forming regardless of the creeping of the strip or the conditions which may affect uniform and true edge forming.
It is also the purpose of the present invention to provide a strip edge monitoring and tracking control system to ensure properly formed edges regardless of camber or other problems noted.
Another problem in pipe and tube mills of the cage type is that the breakdown passes which normally also support the edge forming roll sets also stand in a straight vertical plane perpendicular to the horizontal plane which is defined by the mill floor. Frequently, in such mills the strip extends in a downhill flow from flat to the final tubular or circular form. Somewhat infrequently, the pass may be uphill. Typically, the amount of downhill could be one to two diameters of the pipe. If the breakdown rolls or the edge forming rolls are in a plane vertical to the mill floor, the pressure between the rolls developed may not be enough to do any significant forming. If, however, the top and the bottom rolls are pressed together harder, an unwanted bending or cold forming of the strip develops. In this case the strip is subjected to some unnecessary and harmful stress and strain, and often results in poor forming and welding of the tube, higher energy consumption, and greater stress on the mill components. Thus, if the breakdown roll stands or the edge forming roll stands can be tilted to be at the proper angle with regard to the uphill or downhill movement of the strip, such problems will not occur.